A data storage device such as a magnetic, optical, or magneto-optical drive includes a rotating storage medium. For example, modern disc drives comprise one or more rigid discs that are coated with a magnetically changeable medium and mounted on the hub of a spindle motor for rotation at a constant speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors.
Typically, a stream of data, such as streaming audio or video, is saved on a storage medium of a data storage device such as a disc drive in a Digital Video Recorder (DVR) by writing the data in the stream to the storage medium starting at a beginning address and running consecutively along the same track of the medium. If the stream contains more data than can be stored in a single track, data is typically stored in subsequent, concentric tracks on the medium. Other streams may additionally be stored in other concentric series of tracks on the medium such that the series of tracks for two or more streams form a series of concentric bands around the storage medium.
However, storing a plurality of streams or other large volumes of information in such a manner has some drawbacks. First, the compression technique used for the storage and retrieval of this data will effect the time needed for retrieval to be performed. If the user desires a higher degree of compression, the stored data contains less and less of the information required for retrieval of the information in a random access fashion. For example, when compressing video data, an algorithm that achieves a higher degree of compression does so by reducing the ratio of full frames to partial frames. Therefore, the retrieval system must perform a hunting type search of fewer full frames to find the data requested. This hunting type of search will cause an increase in the latency of the device and degradation in performance.
Second, when streams of data are stored in concentric bands of tracks on the storage medium and more than one of the streams are accessed at any one time, a significant amount of head seeking occurs as data is read from or written to one then another stream. For example, a DVR may store more than one movie. A first movie may be stored in a band of tracks near the outside diameter of the storage medium. A second movie may be stored in a second band of tracks inside the first band. As the first movie is replayed or stored, little if any seeking by the heads may occur. However, if the second movie is started for replay or recording by another viewer, the DVR must now read/write both movies. The result is that the heads of the storage device in the DVR will be required to perform many longer seek operations as they switch between the concentric bands of tracks storing the separate movies. This excessive seeking increases power consumption and reduces throughput of the storage device.
This problem is compounded when storing data near the inner diameter of the storage medium. Since less and less data can be stored per track near the inner diameter, a greater number of tracks are required to store data. This greater number of tracks results in a longer physical distance over which the heads must perform the seek operations.
Additionally, tracks near the inner diameter of the storage medium have a significantly lower data transfer rate than the tracks near the outer diameter of the storage medium. Therefore, storing data streams in concentric bands of tracks results in inefficient allocation of the higher data rates available near the outer diameter of the storage medium.
Accordingly there is a need for a file system that arranges data streams on a storage medium to allow very fast access to any random point within the data stream, to minimize head seeking when reading or writing multiple streams, and to uniformly distribute use of the higher data transfer rate at the outer diameter portions of the storage medium. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.